The present invention relates to a modulated signal transmitting apparatus for receiving modulated signals and sending them out.
A common process of performing remote control on equipment or devices to be controlled involves the following operations. A remote control transmitter modulates a carrier with a command signal and converts the modulated signal by a light-electricity conversion means into an infrared signal, which is transmitted as an infrared remote control signal. The equipment to be controlled receives the infrared remote control signal at the light receiving section, converts it into an electric signal, and demodulates it to recover the command signal. According to the command signal thus recovered, the controlled equipment performs the required control.
When such a remote control system is exposed to intermittent external noise such as from fluorescent lamps, especially when the carrier frequency of the remote control signal is in the same range as the external noise frequency, the remote control signal is interfered with by the noise, with the result that the remote control signal cannot be correctly received by the controlled equipment. The command signal therefore cannot be demodulated and recovered, resulting in an undesired operation of the equipment or failure to operate.
With a view to overcoming the above drawback experienced with conventional transmitters, it is an object of this invention to provide a modulated signal transmitting apparatus which is capable of outputting modulated remote control signals without being affected by external noise.